The present invention relates to a high dielectric constant material used for multilayer wiring boards having a built-in passive element capacitor, and a multilayer wiring board and a module substrate using the said material.
In order to realize high-density surface packaging, many studies have been made for reducing the size of via holes, narrowing down wiring pitch, establishing the build-up system, etc., in the manufacture of the substrates. Efforts have also been made for miniaturization of IC packages, multiplication of pins, miniaturization and surface packaging of the passive parts such as condensers and resistors. On the other hand, with the progress of miniaturization of the passive elements, there arose a problem in that their handling became more difficult in the manufacture and packaging thereof, and the limitation of the conventional technology in this line has become apparent. As a solution to this problem, it has been proposed to form the passive elements directly on the surface or in the inside of a printed wiring board. This makes it unnecessary to mount the passive element chip parts on the printed wiring board, conducing to realize high-density packaging and an enhancement of reliability. The conventional coating and sintering techniques using a paste of a metal or an insulator, such as practiced with the ceramic substrates, can not be directly applied to the other types of substrates, especially organic substrates which are low in heat resistance.
As means for forming the passive elements such as mentioned above on an organic substrate, there have already been proposed the methods comprising coating the substrate with a mixture of an organic polymer and a high dielectric filler (P. Chanel et al, 46th Electric Components and Technology Conference, pp. 125–132, 1996; Y. Rao et al, 2000 Electric Components and Technology Conference, pp. 615–618, 2000), a technique for elevating the packing rate of an inorganic filler such as barium titanate (JP-A-6-172618), and a method using ECR-CVD (electronic cycloton resonance chemical vapor deposition) which is capable of film forming at low temperature (T. Matsui et al, Circuit Technology, Vol. 9, pp. 497–502, 1994).
It is necessary to raise the filler loading for elevating the dielectric constant of the filler applied as a composite with an organic resin. High loading of an inorganic filler in a resin, however, tends to cause formation of voids when the resin is cured, due to bad compatibility of inorganic fillers with resins. Further, because of low interfacial adhesion between inorganic filler and resin, there tends to take place separation at the interface. Therefore, use of a resin composite with high inorganic filler loading as an insulating material raises the concern that reliability be lowered in relation to dielectric strength or leakage current.
Also, the method using ECR-CVD has problems in that a specific apparatus must be used, that it is impossible to form the dielectric films at low cost by a batch process, and that it is difficult to form a dielectric film having a complicate configuration.
On the other hand, as means for increasing the dielectric constant, a method is suggested in which a metal power having an average particle size of not less than several ten μm, which is the standard size of metal powders, is filled in an organic resin. Although such a composite material shows a satisfactory dielectric constant of not less than several ten, it suffers a dielectric loss tangent of not smaller than 0.1 due to skin effect, and more seriously, such an organic resin/metal composite is very low in insulating performance. Further, miscibility of organic resin with metal is bad like inorganic materials.